The present invention relates to a color image forming apparatus realized as, for example, an electrophotography copy machine.
In some of the color image forming apparatuses of this type, toner images of different colors are sequentially formed on a photosensitive drum, and sequentially transferred onto an intermediate transfer medium in a superposed manner. The superposed toner images are simultaneously transferred from the intermediate transfer medium to a sheet of paper.
The development method as disclosed in, for example, Japanese Patent Application KOKAI Publication No. 60-214377 is known as a method for use in color image forming apparatuses. This method is of a so-called revolver type in which a plurality of developing units for different colors are provided on revolving units in the direction of revolution of the revolving units. The revolving units are revolved to align the developing units with a photosensitive drum one by one.
Each developing unit has a developing roller that rotates to supply toner. A predetermined gap is formed between the developing roller and photosensitive drum.
As seen from, for example, FIG. 5, positioning flanges 102, 102 have a diameter which is larger, by a predetermined value, than a photosensitive drum 101. The positioning flanges 102, 102 are provided at the opposite sides of the photosensitive drum 101 such that they are in contact with revolving units 103, 103, thereby defining a predetermined gap between the photosensitive drum 101 and a developing roller 104.
In the prior art, the positioning flanges 102, 102 are in direct contact with the revolving units 103, 103. Therefore, the vibrations of the revolving units 103, 103, which occur when they revolve, are transmitted to the photosensitive drum 101, thereby vibrating the photosensitive drum 101.
If the photosensitive drum 101 is exposed to form an electrostatic latent image while it is vibrating, the resultant electrostatic latent image is blurred, thereby degrading the image quality. To avoid this, in the prior art, an electrostatic latent image cannot be formed until the vibration of the photosensitive drum 101 ceases, with the result that the efficiency of image processing is inevitably reduced.